Aqueous dispersions of polyurethanes with acrylate/methacrylate group modification, known as polyurethane (meth)acrylates, and their use in radiation-curable coating compositions have been known for some time (see, for example, P. Glockner et al. “Radiation Curing for Coatings and Printing Inks” Vincentz Network 2008, pp. 77-80). This relates to polyurethanes based on diisocyanates and polyols that are modified with acrylic or methacrylic groups and that in general, in order to improve their dispersibility, have repeating units with ionic groups and/or polyethylene oxide groups. In order to increase the double bond density and to improve the mechanical properties of the coating, the polyurethane (meth)acrylates are frequently formulated with reactive diluents.
Radiation-curable, water-emulsifiable polyurethane (meth)acrylates are known from, for example, EP 694531 A2, DE 19525489 A1, DE 19810793 A1, DE 19933012 A1, DE 19957604 A1, or EP 1591502 A1.
WO 03/022552 describes aqueous dispersions of radiation-curable polyurethanes which are obtainable by reaction of an isocyanate-terminated polyurethane prepolymer with a hydroxylated acylate. The aqueous dispersions are suitable for producing embossed, coated substrates.
WO 02/034808 relates to photoactivatable coating compositions on a water basis, comprising a) a (meth)acryloyl-functional polyurethane in the form of an aqueous dispersion, containing 5 to 18 wt % of alkaline oxide groups and having a (meth)acryloyl functionality in the range from 2 to 40, and b) a UV initiator.
WO 2014/063920 relates to water-soluble or water-dispersible, radiation-curable urethane(meth)acrylates (A) which are constructed substantially from (a) at least one (cyclo)aliphatic di- and/or polyisocyanate, (b1) at least one (cyclo)aliphatic diol, having a molar mass of less than 700 g/mol, (b2) at least one polyester diol having a weight-average molar mass Mw of 700 to 2000, (c) at least one compound having at least one isocyanate-reactive group and at least one radically polymerizable unsaturated group, (d) at least one compound which has at least one isocyanate-reactive group and at least one acid group, (e) at least one base for at least partial neutralization with the acid groups of component (d), (h1) at least one amine which is substituted by one or two hydrocarbon radicals and in which the hydrocarbon radicals together have at least 12 carbon atoms.